If the subject of your image is radically brighter or darker than its background, you'll want to sit up and pay attention to this section. While blend modes are pretty powerful in their own right (and several of them can pulverize a white or black background instantly), another set of blending options in the Layer Style dialog box (Layer Styles) can eat backgrounds for lunch—nondestructively!
Photoshop gives you a few different ways to open the Layer Style dialog box (Figure 7-20). Once you've selected the image layer you want to work with by clicking it, open the dialog box using one of the following methods:
Double-click its layer thumbnail in the Layers panel.
Click the little fx button at the bottom of the Layers panel and choose Blending Options.
Choose Layer→Layer Style→Blending Options.
The Blending sliders won't work on a locked Background layer; you have to double-click the layer first to make it editable.
At the bottom of the resulting dialog box lie two pairs of sliders (they look like triangles): one set for the This Layer bar and another for the Underlying Layer bar, as shown in Figure 7-20 (top). Each slider lets you make parts of your image transparent based on the brightness value of the pixels. The left slider represents the shadows (blacks) in your image and the right one represents the highlights (whites). If you want to affect the currently active layer, then tweak the This Layer slider (you'll learn about the Underlying ...